The long-range goals of the proposed research are to define the roles of the nuclear and mitochondrial genetic systems in mitochondrial biogenesis and to understand how these roles are coordinated and modulated. The proposed study focuses on mitochondrial ribosome assembly, a process which requires the participation of both genetic systems. Specific aims are: (a) to characterize mutants with defects in mitochondrial ribosome assembly, (b) to characterize processing pathways of mitochondrial rRNAs, (c) to elucidate the role of the mitochondrially-synthesized, mitochondrial ribosomal protein, S-5 in mitochondrial ribosome assembly, and (d) to develop methods for genetic mapping of Neurospora extra-nuclear mutants. The proposed research is intended to provide information about mitochondrial biogenesis and nuclear-mitochondrial interactions which is applicable to all eukaryotic cells.